After Wisconsin's loss to Michigan, there are four teams in the B1G West with one loss: Northwestern (3-1 conf, 3-3 overall); Wisconsin (2-1 / 4-2); Iowa (2-1 / 5-1), and Purdue (2-1 / 3-3).
The way divisional tiebreakers work is: (1) head-to-head result; (2) if three or more teams are tied, the teams' conference records are compared against each other, and then you go back to (1) if that leaves two teams, or look at divisional records if it leaves more than two teams.
Right now, Wisconsin has a head-head edge having beaten Iowa, with @NW (10/27) and @Purdue (11/17) remaining on its schedule, along with a visit to Penn State on 11/10.
Iowa plays at Purdue (11/3) and hosts Northwestern (11/10), and visits Penn State on 10/27.
Northwestern has the easiest conference schedule upcoming, hosting Wisconsin (10/27) and visiting Iowa (11/10), and also plays ND on 11/3.
Purdue hosts Iowa on 11/3 and Wisconsin on 11/17, and plays OSU on 10/20 and visits MSU on 10/27.
So, to me, if you're interested in the West division race, the Northwestern games against Wisconsin and Iowa will be the key ones, as Northwestern has the easiest B1G schedule remaining. Purdue has the toughest schedule remaining. I'd have to say Northwestern and Wisconsin have the inside track of these four teams.
So if Michigan were to manage to get through its remaining opponents—a big "if", we all know—it could be looking at a rematch either way.